Controlled school explosions after hazardous chemical finds
Controlled explosions took place at two Carmarthenshire schools after the discovery of chemicals described as "hazardous".
Guidance was issued nationally, with teachers urged to check if laboratories keep 2,4 dinitrophenyl hydrazine (DNP).
It was discovered at three Carmarthenshire sites in total, with Army explosive ordnance teams visiting.
DNP, used in laboratory tests, is known to pose a risk of explosion by shock, friction or fire and is usually stored inside a larger container holding water.
Controlled explosions took place at Queen Elizabeth High School, Carmarthen and Coleg Sir Gar, Llanelli, on Tuesday and Army teams also attended Ysgol Gyfun Emlyn, Newcastle Emlyn, on Monday.
Dyfed-Powys Police has now issued a warning to all schools and colleges, urging them to check the state of DNP stored in science laboratories.
It says it will help them dispose of it if it is considered "hazardous".
On Monday, 1,500 pupils were evacuated from the Gorseinon campus of Gower College after a discovery.
A Ministry of Defence spokesman said expert military bomb disposal teams have been deployed to support the Department of Education.
He said they are helping to "dispose of chemicals which have been incorrectly stored by a number of secondary schools" in the "safest possible manner".
A controlled explosion also took place at Swansea University last week after a different chemical, picric acid, was found.
Action has also been taken at Clifton College, Bristol, in Bromley, Kent and at a school in West Sussex.